The present invention is directed in general to an apparatus and method for decreasing the locomotive smoke emissions when the operator advances the locomotive throttle position, and more specifically to an apparatus and method that delays the application of load to the engine and modifies engine timing.
Recent amendments to United States environmental statutes and regulations require lowering of the permitted emissions from locomotive diesel engines, including visible smoke. One such requirement is the reduction in NOx emissions, which can be effected by retarding the fuel injection timing of a locomotive diesel engine. But this timing modification negatively impacts fuel consumption and, therefore, it is desirable to increase the engine compression ratio to gain back some of the fuel consumption losses.
However, increasing the compression ratio also increases the visible smoke emissions at partial engine loading. The problem of visible smoke is especially acute during transient load and speed changes, i.e., when the locomotive operator advances the throttle (i.e., moves the throttle to a higher notch position) to call for higher speed and/or greater load pulling capacity (i.e., locomotive horsepower). The smoke emissions tend to be worse when the throttle is advanced to higher throttle positions when starting from lower positions.
In the prior art locomotives, when the throttle is advanced from one position to the next (where the throttle positions are commonly referred to as notches) the diesel engine speed and the load (or current excitation) applied to the traction motors are simultaneously increased to the speed and horsepower point of the new notch position. In response to the notch position change the engine acceleration to the new speed point is controlled by an electronic governing unit. Also, the locomotive control system applies more excitation current to the main alternator, which in turn supplies more current to the traction motors, increasing the motor horsepower. While the speed and load are increasing to their new respective points, the fuel injection timing is determined from a look-up table based on engine speed. As discussed above, during these notch or transient changes, undesirable smoke emissions are produced.
In the prior art locomotive systems, the electronic governing unit acts as the speed governor in response to speed changes requested by the locomotive control system. In the prior art, the speed governor does not receive a signal from the throttle when it is changed from one notch position to another and therefore does not know when a notch change has occurred; the speed governor knows only the engine speed demand. In fact, there are multiple notch settings that vary the horsepower delivered by the traction motors, but not the engine speed.